Check out www.mapmyrun.com

This is a nifty little website to figure out the mileage of your outdoor walk or run. You can use their map to find your start location and then trace your route. It calculates your distance. You can zoom in so that your route is very accurately entered. They have satellite images for my neighborhood, so I could zoom in and even tell where the sidewalks are. Check it out at www.mapmyrun.com.